Loss-of-Function Variant in the SMPD1 Gene in Progressive Supranuclear Palsy-Richardson Syndrome Patients of Chinese Ancestry

[Acid sphingomyelinase deficiency: A review]

Acid sphingomyelinase deficiency, formerly known as Niemann-Pick disease types B, A/B, and B, is a rare genetic disorder. It is an inherited autosomal recessive disease, linked to mutations in the SMPD1 gene. It is a lysosomal storage disease that leads to the accumulation of sphingomyelin mainly in macrophages, resulting in a multisystemic phenotype, primarily manifesting as hepatosplenomegaly and pulmonary involvement. The central nervous system may be affected, depending on the phenotype. Indeed, there is a phenotypic continuum among the three main forms that are distinguished: a chronic visceral form (formerly known as Niemann-Pick disease type B), a chronic neurovisceral form (intermediate form formerly known as Niemann-Pick disease type A/B), and an infantile neurovisceral form (formerly known as Niemann-Pick disease type A). The estimated overall prevalence is from 1 in 100,000 to 1 in 1,000,000 births. Clinical manifestations, as well as the age of onset of symptoms and/or diagnosis, vary depending on the form. The rarity of the disease and its nonspecific symptoms explain the diagnostic delay or failure to recognize the disease. Knowing and recognizing this disease is important, especially since there is an effective specific treatment through enzyme replacement therapy. In this article, we describe the clinical manifestations of acid sphingomyelinase deficiency, to understand when to suspect it, how to confirm it, and how to manage it.

The Genetic Background of the Immunological and Inflammatory Aspects of Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative disease, classified as an atypical Parkinsonian syndrome, that has been pathologically and clinically defined. The histopathological aspects of the disease include tufted astrocytes, while the clinical features involve oculomotor dysfunction, postural instability, akinesia, cognitive impairment, and language difficulties. Although PSP is generally considered a sporadic disease, interest is growing in its genetics, with contemporary research focusing on familial backgrounds and neuroinflammation. Indeed, microglial activation and other inflammatory mechanisms of PSP pathogenesis have been extensively analyzed using genetic examinations to identify the factors impacting neurodegeneration. As such, this review aims to elaborate on recent findings in this field.

Genetic-based diagnostics of Parkinson's disease and other Parkinsonian syndromes

INTRODUCTION

Parkinson's disease (PD) is a complex disorder with vast clinical heterogeneity. Recent genetic, imaging and clinical evidence suggest that there are multiple subtypes of PD, and perhaps even distinct clinical entities, which are being diagnosed under the umbrella of PD. These might have similar clinical presentation, but potentially different underlying mechanisms, which, in future, will require different treatments. Despite extensive genetic research progress, genetic testing is still not a common practice in clinical patient care.

AREAS COVERED

This review examines the numerous genes that have been discovered to affect the risk of, or cause, PD. We also outline genetic variants that affect PD age at onset, its progression, and the presence or severity of motor and non-motor symptoms. We differentiate between PD, other synucleinopathies, and atypical parkinsonism syndromes, and describe genes responsible for familial forms of typical PD and atypical parkinsonism. Lastly, we present current clinical trails that are underway for targeted therapies, particularly for GBA1-PD and LRRK2-PD which are the most significant subtypes.

EXPERT OPINION

While genetic studies alone cannot be diagnostic for PD, proper utilization of genetic screening for PD could improve diagnostic accuracy and predictions for prognosis, guide treatment, and identify individuals that qualify for clinical trials.

Identification of Genetic Variants in Progressive Supranuclear Palsy in Southeast Asia

BACKGROUND

Progressive supranuclear palsy (PSP) is largely a sporadic disease with few reported familial cases. Genome-wide association studies (GWAS) in sporadic PSP in Caucasian populations have identified MAPT as the most commonly associated genetic risk locus with the strongest effect size. At present there are limited data on genetic factors associated with PSP in Asian populations.

OBJECTIVES

Our goal was to investigate the genetic factors associated with PSP in Southeast Asian PSP patients.

METHODS

Next-generation sequencing (whole-exome, whole-genome and targeted sequencing) was performed in two Asian cohorts, comprising 177 PSP patients.

RESULTS

We identified 17 pathogenic or likely pathogenic variants in 16 PSP patients (9%), eight of which were novel. The most common relevant genetic variants identified were in MAPT, GBA1, OPTN, SYNJ1, and SQSTM1. Other variants detected were in TBK1, PRNP, and ABCA7-genes that have been implicated in other neurodegenerative diseases. Eighteen patients had a positive family history, of whom two carried pathogenic MAPT variants, and one carried a likely pathogenic GBA1 variant. None of the patients had expanded repeats in C9orf72. Furthermore, we found 16 different variants of uncertain significance in 21 PSP patients in PSEN2, ABCA7, SMPD1, MAPT, ATP13A2, OPTN, SQSTM1, CYLD, and BSN.

CONCLUSIONS

The genetic findings in our PSP cohorts appear to be somewhat distinct from those in Western populations, and also suggest an overlap of the genetic architecture between PSP and other neurodegenerative diseases. Further functional studies and validation in independent Asian cohorts will be useful for improving our understanding of PSP genetics and guiding genetic screening strategies in these populations. © 2024 International Parkinson and Movement Disorder Society.

Parkinson's Disease is Predominantly a Genetic Disease

The discovery of a pathogenic variant in the alpha-synuclein (SNCA) gene in the Contursi kindred in 1997 indisputably confirmed a genetic cause in a subset of Parkinson's disease (PD) patients. Currently, pathogenic variants in one of the seven established PD genes or the strongest known risk factor gene, GBA1, are identified in ∼15% of PD patients unselected for age at onset and family history. In this Debate article, we highlight multiple avenues of research that suggest an important - and in some cases even predominant - role for genetics in PD aetiology, including familial clustering, high rates of monogenic PD in selected populations, and complete penetrance with certain forms. At first sight, the steep increase in PD prevalence exceeding that of other neurodegenerative diseases may argue against a predominant genetic etiology. Notably, the principal genetic contribution in PD is conferred by pathogenic variants in LRRK2 and GBA1 and, in both cases, characterized by an overall late age of onset and age-related penetrance. In addition, polygenic risk plays a considerable role in PD. However, it is likely that, in the majority of PD patients, a complex interplay of aging, genetic, environmental, and epigenetic factors leads to disease development.